Defect Characterization of the SiO₂/Si Interface Investigated by Drift-Assisted Positron Annihilation Lifetime...

Area of Science:

• Materials Science
• Solid State Physics
• Surface Science

Background:

• Positron annihilation lifetime spectroscopy (PALS) is a powerful technique for probing defects in materials.
• Understanding defects at the silicon-dioxide/silicon (SiO2/Si) interface is crucial for semiconductor device performance.
• Applied electric fields can influence charged particle transport, but their effect on positron behavior near interfaces is less explored.

Purpose of the Study:

• To investigate the influence of an applied electric field on positron spatial distribution and annihilation characteristics in a p-type (100) silicon metal-oxide-silicon (MOS) capacitor.
• To determine positron drift-transport parameters and analyze the impact of electric fields on positron trapping at the SiO2/Si interface.
• To characterize the nature of defects on both sides of the SiO2/Si interface and their dependence on MOS device operation.

Main Methods:

• Drift-assisted positron annihilation lifetime spectroscopy (PALS) was performed on a p-type (100) silicon MOS capacitor.
• The applied electric field was varied to induce accumulation, depletion, and inversion conditions.
• Positron lifetime spectra were analyzed to extract drift-transport parameters and defect information.

Main Results:

• The internal electric field effectively controlled positron drift, either enhancing or hindering their diffusion towards the SiO2/Si interface.
• Key positron drift-transport parameters were successfully derived from the lifetime data.
• Distinct defect types, void-like and vacancy-like (Pb centers), were identified on opposite sides of the interface.
• The trapping behavior of Pb centers was found to be dependent on the charge state, which varies with the MOS device operation mode.

Conclusions:

• Drift-assisted PALS is effective in probing the complex behavior of positrons and defects at the SiO2/Si interface.
• The SiO2/Si interface exhibits asymmetric defect characteristics, with different defect types on the silicon and oxide sides.
• The charge state modulation of interface defects under varying electric fields significantly impacts positron trapping, providing insights into defect dynamics.